Mechanized separation of mixed solid waste and recovery of recyclable products

ABSTRACT

The method and systems efficiently extract recyclable materials from a mixed solid waste stream. The methods and systems use sizing, density and dimensional separation to produce intermediate waste streams that are enriched in particular recyclable materials. The recyclable materials can then be efficiently sorted from the individual intermediate streams using mechanized sorting equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/693,763, filed Dec. 4, 2012, which is a continuation of U.S.application Ser. No. 13/221,647 filed Aug. 30, 2011, titled “MECHANIZEDSEPARATION OF MIXED SOLID WASTE AND RECOVERY OF RECYCLABLE PRODUCTS,”now U.S. Pat. No. 8,322,639, which claims the benefit of U.S.Provisional application 61/417,216 filed Nov. 24, 2010, titled“MECHANIZED SEPARATION OF MIXED SOLID WASTE AND RECOVERY OF RECYCLABLEPRODUCTS.” Application Ser. No. 13/693,763 is also acontinuation-in-part of U.S. application Ser. No. 13/221,637 filed Aug.30, 2011 Titled “MECHANIZED SEPARATION OF MIXED SOLID WASTE AND RECOVERYOF RECYCLABLE PRODUCTS,” which claims the benefit of U.S. ProvisionalApplication 61/417,216 filed Nov. 24, 2010. All of the foregoingapplications are hereby incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to systems and methods for recoveringrecyclable materials from solid waste streams such, but not limited to,municipal solid waste.

2. The Related Technology

Commercial, industrial, and residential consumers generate large amountsof throw-away and waste products (i.e., municipal solid waste) that needto be handled and disposed of in an environmentally satisfactory manner.Traditionally, municipal solid waste (hereinafter “MSW”) has beendisposed of by landfilling or incineration. However, these methods ofwaste product disposal contaminate the soil, water and air.Environmental restrictions as well as land usage demands for housinghave reduced the number of sites available for landfills.

In response, governments and the public have demanded that, whereverpossible, recycling systems should be employed to conserve materialresources and to reduce pollution problems. Efforts have been made torecover valuable resources such as glass, plastic, paper, aluminum, andferrous and non-ferrous metals from waste materials. For example,households in many cities are asked to sort their garbage intorecyclables (e.g., paper, plastic containers, metal containers and glasscontainers) and non-recyclables. However, rates of non-compliance andmis-compliance are high. Some people fail to sort their waste at all andother sort it incorrectly, which either shunts recoverable materialsinto the waste stream or contaminates the recyclable stream with wastematerials. Non-compliance and mis-compliance reduce the efficiency ofand increases the costs associated with operating recycling systemsdesigned to processed pre-sorted waste.

Some recycling systems attempt to avoid the problems with presortedwaste by attempting to recover recyclable materials from mixed waste.However, many of these systems are fraught with the tendency to behighly labor intensive to operate, while offering relatively lowrecovery rates of recyclables.

The energy balance of many recycling systems is sub-par or, in somecases, negative. Some recycling systems are so inefficient that theprocesses of recovering, transporting, and recycling the recyclablematerials consumes more energy than could be saved by simply landfillingthe garbage and making new products from raw materials. In other cases,so little of the recyclable materials are recovered that the problemswith waste stream disposal go essentially unmitigated.

SUMMARY

The present disclosure relates to methods and systems for mining highvalue recyclable materials from a mixed solid waste stream. The methodand systems can use sizing and density separation to produceintermediate waste streams that can be properly sorted to extract largepercentages of valuable recyclable materials. The sizing and densityseparation produce intermediate streams that are enriched in particularrecyclable materials. The recyclable materials can then be efficientlysorted from the individual intermediate streams using mechanized sortingequipment.

In addition to sizing and density separation, the flow of waste materialmay be metered throughout all or a portion of the system to ensure anacceptable flow rate and/or burden depth in the equipment. Proper massflow and burden depth facilitates efficient extraction of the recyclablematerials in the mechanical sorting equipment.

The systems and methods described herein can handle large volumes ofhighly variable mixed waste materials. The systems and methods canefficiently extract recyclables from unsorted mixed waste (e.g., blackbin MSW), home-sorted recyclable streams where mis-compliance is high(e.g., blue bin MSW), and other types of MSW such as variable commercialsolid waste streams from retail establishments, light manufacturing,warehouses, office buildings, etc., and industrial waste streams. Themethods and systems described herein can recover significantly largerpercentages of different types of recyclable materials from variablewaste streams as compared to known systems. This ability is due in largepart to the sizing, size separation, density separation, and dimensionalseparation, which creates a concentrated, homogenous intermediate wastestreams from which recyclables can be mechanically extracted. Unliketraditional refuse derived fuel plants, the methods and systems of theinvention fractionate and spread the waste material sufficiently toprepare the intermediate streams for efficient sorting in mechanicalsorters such as optical sorters and eddy current sorters, anddimensional sorters such as ballistic separators and angled discscreens.

The need to efficiently extract multiple types of recyclable materialsfrom variable mixed waste streams is a long-felt but unmet need. Theinability of the industry to extract significant percentages ofdifferent types of recyclable materials from variable mixed wastestreams has resulted in well-known political campaigns throughout muchof the world to teach the lay population that it is their responsibilityto hand sort recyclables at the time of generation and then disposal.Due to natural human behavior, these efforts, while laudable, have notresulted in desired recycle rates. The vast majority of recyclable wastematerials continue to be poorly recovered and/or utilized. The methodsand systems described herein meet this long felt and unmet need byefficiently recovering recyclables using mechanical devices that arearranged and configured to efficiently handle a varied solid wastestream. In addition, traditional curbside residential recycling programsand commercial recycling programs require expensive and pollutingseparate collection routes and vehicles. Furthermore, once collected byseparate vehicles, the materials still need to be separated and therecyclables recovered in traditional Material Recovery Facilities(MRFs). This is highly inefficient and costly.

These and other features of the embodiments disclosed herein will becomemore fully apparent from the following description and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only illustrated embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 is a flow diagram illustrating methods for recovering recyclablematerials from a mixed solid waste stream;

FIG. 2 illustrates a cut-away view of an air drum separator adapted foruse in the system for separating solid waste, according to oneembodiment of the present invention; and

FIG. 3 is a flow diagram illustrating a system for separating solidwaste, according to yet another embodiment of the present invention.

DETAILED DESCRIPTION

I. Methods for Mining Recyclables from Solid Waste Streams

FIG. 1 illustrates an example method 100 for recovering recyclablematerials from a mixed solid waste stream. In one embodiment, method 100includes (i) in a first step 102, providing a mixed waste streamincluding recyclable materials such as paper, plastic, and metal(particularly non-ferrous metal); (ii) in a second step 104, comminutingthe mixed waste stream; (iii) in a third step 106 fractionating themixed waste stream by size to produce a plurality of sized wastestreams; (iv) in a fourth step 108, fractionating at least a portion ofthe sized waste streams by density to produce a plurality ofintermediate waste streams individually enriched in one or more of therecyclable materials; (v) in a fifth step 110, individually sorting theplurality of intermediate waste streams using one or more sortingapparatuses to produce recyclable products such as, but not limited torecycled paper products, recycled plastic products, and/or recycledmetal products. Optionally the method can include metering 112 and/orspreading the sized waste streams throughout any or all portions ofprocess 100 to control mass flow and/or burden depth.

In the present disclosure, a number of comminuting and/or sizefractionation steps are described with respect to methods and systemsfor the separation of solid waste. Typically each of these steps has anassociated size cut-off. Persons having skill in the art will appreciatethat fractionated materials typically exhibit a distribution ofparticles. The distribution will often include an insignificant numberof particles above or below the cut-off. Unless otherwise specified, anupper cut-off number (e.g., 16″ or less, 12″ or less, 8″ or less, theupper range of an 8″ to 2″ over fraction) generally means that about 90%of the particles in the fraction (i.e., the distribution) have a size ofless than the cut-off number, while about 10% of the particles in thefraction will be larger than the upper cut-off size. Unless otherwisespecified, a lower cut-off number (e.g., the lower range of an 8″ to 2″over fraction) generally means that about 90% of the particles in thefraction have a size of larger than the cut-off number, while about 10%of the particles in the fraction are smaller than the lower cut-offsize. In alternative embodiments, upper cut-off number can include 95%or 99% of the of the particles in the fraction and/or the bottom cut caninclude less than 5% or less than 1% of the particles in the fraction.

1. Providing Solid Waste Stream

The waste streams utilized in the methods and systems described hereininclude a mixture of different types of solid materials. The wastestream includes recyclable materials that upon separation from othertypes recyclable material or refuse can be utilized and therefore havevalue. In one embodiment, the mixed solid waste may be Municipal SolidWaste (“MSW”) (i.e., trash or garbage). MSW is a type of waste materialthat includes predominantly household waste with sometimes the additionof commercial and/or industrial wastes collected by a municipality or acontractor hired by a municipality or by commercial and/or industrialbusinesses within a given area. Commercial solid waste is type of wastesuch as trash that is generally collected from businesses such as officebuildings or business establishments. Industrial solid waste isgenerally found in heavy manufacturing industries. MSW and commercialwaste generally does not include industrial hazardous waste. The mixedwaste can be “black bin” waste in which little or no removal ofrecyclable material has been performed by the source of the waste oralternatively may be a recycled or “blue bin” waste that includes amixture of recyclable waste materials (also referred to as “singlestream waste”). The single stream waste may be commercial or residentialand may have low or high mis-compliance.

Mixed waste contains a number of components that only have value as arecyclable material when separated from other components. Theserecyclable materials can include plastics; fiber materials, includingpaper and cardboard; metals, including ferrous metals and non-ferrousmetals such as brass and aluminum; glass; textiles; rubber; and wood.Preferably the waste stream includes 1, 2, 3, or more high valuematerials including, but not limited to one or more of paper, plasticand non-ferrous material.

While even small percentages of these materials may be valuable,separating the recyclables from each other and other components in mixedsolid waste streams is extremely challenging. This is especially truewhen two, three, four, or more different types of recyclables need to beseparated and recovered. Mixed commercial and residential wastes maycontain large amounts of non-recyclable waste materials such as food andkitchen waste; green waste, such as yard clippings, plants, vegetation,branches, and the like; and inorganic wastes, such as concrete, dirt,rocks, and debris.

The methods and systems describe herein include providing a mixed solidwaste stream that includes at least one recyclable material, preferablyat least two, and more preferably at least 3 different types ofrecyclable materials. In one embodiment, the waste stream includes atleast two materials selected from the group of paper, plastic and metal.Preferably, the mixed waste stream includes paper, plastics, and metals.

The amount of recyclable materials in the stream, the percentage of therecyclable material recovered, and the value of the recycled materialhave a significant impact on the economic viability of extracting therecyclable materials through mechanized sorting (larger values beingmore desirable).

In one embodiment, the mixed waste stream may include at least 0.5%, 1%,2%, 3%, 4%, 5% of a recyclable metal or less than 30%, 20%, 15%, 10%, or5% (by weight) or a range of any of the forgoing upper and lower weightpercents of recyclable metal material.

The mixed waste stream may include at least 2.5%, 5%, 7.5%, or 10% of arecyclable plastic material or less than 60%, 40%, 20% (by weight) or arange of any of the foregoing upper and lower weight percentages ofrecyclable plastic material.

The mixed waste stream may include at least 5%, 10%, 15%, 20%, 25%, or30% of a recyclable mixed paper material or less than 80%, 70%, 60%, 50%or 40% (by weight) or a range of any of the foregoing upper and lowerweight percentages of mixed paper material.

The mixed waste stream may include at least 15%, 25%, 35%, of arecyclable dry organic material and less than 80%, 70%, 60%, 50% or 40%(by weight) or a range of any of the foregoing upper and lower weightpercentages of dry organic material. The mixed waste stream may includewet organic waste, dry organic waste, and/or inorganic waste. In oneembodiment, the weight percentage of wet organic waste, dry organicwaste, and inorganic waste in the mixed waste stream is each(independent of one another) at least 5%, at least 10%, at least 20%, atleast 50%, or at least 75% (the sum of the three weight percentages notexceeding 100%).

In one embodiment, the mixed solid municipal waste may be an unprocessedmunicipal waste. For example, solid waste stream may be provideddirectly from a municipal garbage collection process. Alternatively,solid municipal waste may be partially pre-processed (e.g., by homeowners) to remove a portion of the recyclable and/or recoverablematerials. For example, solid municipal waste may be derived from acomprehensive residential or commercial waste stream that contains theremnant materials that exclude source separated materials collectedthrough recycling programs in which a portion of certain recyclables(e.g., mixed paper, newspaper, cardboard, plastics, ferrous andnon-ferrous metal and/or glass containers) have been removed (i.e., theMSW may be a post-recycled waste).

In either case (i.e. methods using unprocessed MSW or source separatedMSW), the mixed waste may be manually pre-sorted to recover and removeitems that are difficult to shred or grind, obviously hazardous, and/orthat are particularly large (i.e., easily separated) and have a highrecovery value. The presorting may be performed by loading waste intothe system or may be carried out by personnel on a dedicated presortingline. For example, waste may be metered onto a presorting conveyor wheremanual labor identifies items to be pre-sorted. Typically presorteditems will include items that could damage or cause excessive wear tothe shredder or grinder. Examples include automobile engine blocks,structural steel, tire rims, propane tanks, concrete blocks, largerocks, and the like. Hazardous waste is preferably removed beforegrinding to avoid contamination with other materials in the mixed waste.Examples of obviously hazardous waste include containers of solvents andchemicals, paint cans, batteries, and the like.

Presorting can also be used to recover particularly large and valuableitems that are easily picked from the mixed waste stream. Typically therecyclables recovered in the pre-sorting will be items that are severaltimes larger than the burden depth of the process stream such that theyare easily visible and efficiently removed manually. For example largecardboard boxes (e.g., corrugated containers), structural metal pieces,and electronic waste (e.g. eWaste) can be recovered in presorting. Thepercentage of materials in the mixed waste stream described above referto percentage of the waste stream immediately before it undergoescomminution and/or sizing (i.e., after presort).

As mentioned, the methods described herein allow for recyclablematerials to be mechanically sorted from municipal solid waste even whenthe waste includes large percentages of non-recyclable materials. In oneembodiment the solid waste stream includes at least 20%, 25%, 35%, 50%,or 75% of one or more low value materials. The low value materials arematerials that make separation of the high value materials difficult andthat by themselves are generally not economical to separate. In oneembodiment the low-value materials can be selected from the groupconsisting of, wet organics, green waste, food waste, grit, fines lessthan 1 inch, asphalt, concrete, textiles, and wood, rubber, filmplastic, PVC, foil, rock, used consumer products, low value glass (glasstoo distant from a recycler), composite materials (e.g., tennis shoes),other materials typically found in solid waste, and combinations ofthese. The methods described herein overcome the long felt but unmetneed to economically recover (i.e., mechanically sort) all or a portionof the valuable recyclables in these hard-to-handle waste streams. Theindividual low value materials can be in the solid waste stream in aconcentration of at least 5%, 10%, 15%, 20%, or more.

Those skilled in the art will recognize that the composition of solidwaste streams varies substantially over short periods of time. Of allthe variability found in MSW, there are three constant characteristicsin varying degrees or percentages; density, dimension (2-D or 3-D) andmoisture content. This invention, in part, uses a variety of equipmentthat separates by size, density and dimension, and then directs materialto equipment that separates or recovers by material type (e.g. resintype for plastic, ferrous metal, non-ferrous metals, glass, paper,etc.). For purposes of this invention, the percentage of a particulartype of material within the waste stream can be calculated according toacceptable industry standards such as the 2011 Waste Disposal Guidelinespublished by the California Department of Resources Recycling andRecovery (Also known as “CalRecycle” and previously known as theCalifornia Integrated Waste Management Board), which is herebyincorporated by reference (available atwww.calrecycle.ca.gov/wastechar/YourData.htm#Step1 and the linksassociated therewith). At a minimum sampling of a waste stream shallinclude analyzing samples of at least 200 lbs and sampling on aplurality of different days, weeks, and/or months.

2. Comminution

Optionally the mixed municipal solid waste is conveyed to a comminutingdevice such as grinder or shredder (step 104). Comminution (e.g.,shredding or grinding) may be carried out to improve the efficiency ofsize separation and density separation. In one aspect, the conveyor instep 104 may include a metering system such as a metering wheel or othersuch material leveling or spreading device configured for controllingthe flow and associated burden depth of MSW such that a relativelyconstant and evenly dissipated amount of material is spread across thefull width of the conveyor, at a consistent burden depth or height, andfed to the grinder or shredder over time (and optionally a pre-sortconveyor).

Shredded or ground waste will have a range of particle sizes. In oneembodiment the comminuted waste stream has a upper cut of 16 inches orless, 14 inches or less, 12 inches or less, 10 inches less, or 8 inchesor less or a bottom cut greater than 1 inch 2 inch, 4 inch, or 6 inch,or may have a distribution with an upper cut and lower cut of any of theforegoing upper and lower cuts for the comminuted waste. In oneembodiment, the ratio of the upper cut to lower cut may be less than 8,6, or 4.

The size distribution of any particular fractured material generallydepends on its material properties. For example, some objects likeshipping pallets or tires will be ground or shredded to relatively largeparticle sizes. In contrast, brittle materials like glass, which tend toshatter, and food waste, which tends to easily shred, will be quitesmall after comminution.

The shredder or grinder used to comminute the mixed waste stream mayinclude one or more shafts that include a number of cutting heads thatthat can cut and/or shred incoming waste materials to a selected size.Waste materials may be ground or shredded by turning rotors mounted withcutting blades or knives against a rigid blade housing, they then dropthrough the grinder or shredder to the screen basket (circular punchplate or finned design screens). Materials having a ground cut size lessthan a selected size, drop through a screen and move onto the next stepin the process. Objects that are too large to pass through the screenare typically recirculated repeatedly through the grinder or shredderuntil they are ground to a size that can pass through the screen.

A number of solid waste grinders or shredders available in themarketplace are either adapted or can be adapted for comminuting theinitial solid waste stream. For example, Vecoplan, LLC of High Point,N.C. makes a number of solid waste shredders that can be incorporatedinto the system and used in the methods described herein.

Preferably, the comminuted waste from comminuting device is ground orshred to a size of less than 18 inches, 16 inches, 12 inches, 10 inches,or 8 inches and greater than 2 inches, 4 inches, 6 inches, 8 inches, 10inches, or a range from any of the forgoing upper and lower cutoffsizes. Comminuting the mixed MSW prior to size separation and densityseparation will increase the separation efficiencies of the densityseparators.

3. Size Separation

The comminuted waste may be conveyed to a size separator thatfractionates the mixed waste by size (step 108) to produce two or moresized waste stream (e.g., at least an over fraction and an underfraction).

The sizing may be carried out to produce sized waste streams with aparticular desired particle size distribution to facilitate densityseparation and to produce intermediate streams enriched in particularrecyclable materials. Those skilled in the art will recognize that thecomminuted waste stream can be analyzed to determine size cutoffs inwhich the fractions of the stream separate different types of materialsinto different streams while concentrating similar types of waste intosomewhat concentrated streams. In addition, the sized waste streams maybe optimized for density separation by creating sized waste stream witha narrow distribution of particles.

In one embodiment, the sized waste streams may have a size distributionwith a ratio of small particles to large particles of less than about 10(i.e., the ratio of the upper cut-off to the lower cut-off has a ratioless than about 10), more preferably, less than about 8, 6, or 4. Anunder fraction from size separation may have a top size cut-off of lessthan about 6 inches, 5, inches, 4 inches, 3 inches, or two inches andgreater than 0.5 inch, 1 inch, 2 inch, or 3 inch, or a range within anyof the foregoing upper and lower values for the top size cut. The upperfraction may have an upper size cutoff less than 16, inches, 12 inches,10 inches, 8, inches or six inches and a lower size cutoff greater than2 inches, 4 inches, 6, inches, or 8 inches or a range within any of theforegoing upper and lower cutoffs.

Suitable examples of a size separator that can be used in the presentmethod include a disc screen separator with rubber or steel discs, afinger screen separator, a trommel screen separator, a vibratory screenseparator, a waterfall screen, oscillating screen, flower disc screens,and/or other size separators known in the art.

A disc screen employs a series of rolling shafts having a series ofattached discs with spaces between the discs that objects can fallthrough. The rolling of the shafts creates a wavelike action thatagitates the incoming material as it is conveyed forward. This agitationreleases smaller materials through the screen openings and isaccomplished without vibration or blinding. The disc screen designgreatly reduces the possibility of jamming or seizing during operation.Trommels, vibratory, or finger screens, waterfall screens, oscillatingscreens, flower disc screens, and/or other size separators known in theart also accomplish the same type of size separation objective, whileusing somewhat different engineered designs. Various size separatorsuseful in the invention are commercially available through manydifferent manufacturers worldwide. For example, disc screens, trommelscreens, vibratory screens and waterfall screens are available fromVecoplan, LLC of High Point, N.C.

4. Density Separation to Produce Intermediate Streams

One or more of the sized waste streams are separated by density toproduce intermediate waste streams that are individually enriched in oneor more recyclable materials. Although not required, the densityseparation is preferably performed in a separate apparatus downstreamfrom the size separator. Downstream density separation allows distinctdensity separators to be used on individual sized fractions, whichallows the individual density separators to be configured for particularmaterials and streams. The density separator units may be calibrated toprovide separation between particular materials in the mixed wastestream. Density separation can be used to separate different types ofmaterials such as wet organics, dry organics, and inorganic materials,thereby enriching one or more particular intermediate streams in one ormore different types of recyclable materials.

In mixed municipal waste streams, inorganic waste, wet organic waste,and dry organic waste often exhibit densities within particular ranges.For example, dry organics tend to have a density of greater than 1.0lbs/cubic foot and less than about 12 or 15 lbs/cubic foot; wet organicstend to have a density greater than 8, 10, or 12 lbs/cubic foot and lessthan about 60, 80, or 100 lbs/cubic foot; inorganic materials tend tohave a density greater than about 80 or 100 lbs/cubic foot. Thus, bysetting the density separators accordingly, the wet organic, dryorganic, and inorganic fractions may be separated based on density.Similarly, particular types of recyclable materials such as wood andtextiles will often fall within a certain density range and can beselectively enriched in an intermediate waste stream. While theforegoing densities are useful for many municipal waste streams, thoseskilled in the art will recognize that the teachings provided herein canbe used to analyze any waste mixed solid waste stream and determinedensity cutoffs that will generate intermediate waste streams enrichedin recyclable materials.

In some embodiments, a series of density separators can be used tofurther fractionate the intermediate waste streams. In downstreamdensity separators, the density cutoff is selected to fractionate eitherthe lower or the upper fractions received from the upstream densityseparator. Additional size separation may also be carried out on densityseparated streams. Size and density separation are carried out until theintermediate stream is sufficiently enriched and homogenous in aparticular recyclable material to allow efficient extraction of therecyclable material using mechanized sorting equipment.

Referring now to FIG. 2, an example of a density separation unit that isadapted for separating municipal solid wastes by density is shown. FIG.2 illustrates an air drum separator 200. The air drum separator 200includes an input conveyor 204, a blower 206, a rotating drum 210, anoutput conveyor 222, a heavy fraction conveyor 218, and a light fractionconveyor 226. Mixed density wastes 202 are fed in on the input conveyor204. As the waste material 202 is fed in, it drops off the end of theconveyor 202 where the wastes 202 encounter a stream of moving air 208from the blower 206.

The heavy fraction 216 is separated from the mixed waste material 202 byvirtue of being too heavy to be lifted by the airstream 208. The heavyfraction thus falls down in front of the drum 210 and falls on to theheavy fraction conveyor 218. In contrast, the lighter wastes are liftedup by the airstream 208 and carried over the rotating drum 210 andcarried forward either by the airflow 220 or by the conveyor 222. Thelight fraction 224 drops off the end of conveyor 222 and onto the lightfraction conveyor 226. These machines are highly adjustable to alter theweight density separation coefficient, as desired.

The relative density of the heavy fraction 216 and the light fractions224 can be adjusted by controlling the airflow through the air drumseparator 200. The velocity of the airflow and the volume of air passingthrough the drum separator 200 can be controlled either by increasing ordecreasing the velocity of fan 206 or by opening or closing valve 212.In general, opening valve 212 and/or increasing the velocity of the fan206 will carry heavier objects over the drum 210 such that the lightfraction will have a higher average mass. Likewise, closing valve 212 orlowering the velocity of the fan 206 will cause the heavy fraction 216to have a lower average mass and the light fraction 224 will have alower average mass because only the lighter objects will be carried overthe drum 210. Density separators suitable for use in the presentinvention include, but are not limited to air separators available fromWesteria Fördertechnik GmbH, Ostbevern, Germany. While the particularexample illustrated in FIG. 2 may be preferred in some embodiments,other separators can be used, including density separators that do notinclude drums (e.g., gravity/air separators, windshifters, windsifters,air knifes, etc.).

Density separators like those illustrated in FIG. 2 work best when theratio between the largest and smallest objects being fed into thedensity separator is relatively narrow. Accordingly, it is preferablethat the ratio of the largest to smallest objects that are fed into thedensity separators in the methods and systems described herein be about12 to 1, about 10 to 1, about 8 to 1, 6 to 1, or about 4 to 1. Mostpreferably, the ratio of the largest to smallest objects that are fedinto the density separators in the methods and systems described hereinis about 6 to 1 (i.e., where the ratio of the top-cut to the bottom cutare in the foregoing ratios). In one embodiment, the methods and systemsof the present invention are designed to provide waste materials to thedensity separators with particles size ratios within these approximateranges.

5. Sorting Recyclable Materials from Intermediate Streams

The methods described herein also include extracting a plurality ofrecyclable materials from the intermediate waste stream using one ormore mechanized sorting apparatuses. The particular mechanized sortingapparatus used depends on the particular recyclable material to beextracted.

In one embodiment, the intermediate waste stream may be enriched inmetal, including a ferrous metal and/or a non-ferrous metal. To extracta non-ferrous metal an eddy current separator can be used. The eddycurrent separator can recover non-ferrous metals such as aluminum, brassand copper. Alternatively, or in addition, the metals may includeferrous metal and one or more magnetic separation devices can bepositioned downstream of the density separator and configured to collectferrous metal. Examples of magnetic separators include drum magnets,cross-belt magnets, head pulley magnets, and the like. Optical sorters,stainless steel sorters, infrared sorters, camera sorting machines,induction sorters, metal detection systems, X-ray sorters and the likecan be used to separate different types of metals from one another, toproduce a recyclable product. The recyclable metal products produced inthe methods and systems described herein can be selected from the groupincluding non-ferrous recyclable products such as aluminum, brass, andcopper and/or other metals such as iron and/or stainless steel.

In one embodiment, the sorting apparatus may be a dimensional sortersuch as a 2D-3D sorting apparatus. Examples of 2D-3D sorters includeballistic separators and/or screens configured to separatetwo-dimensional items from three-dimensional items. Two or moreballistic separators and/or screens can be used in series or parallel.The dimensional separators can be used to recover one or more materialsthat are comingled with another material having a similar density, buthaving substantially different dimensional properties (other than size).For example, in one embodiment, the 2D-3D separator may be used toseparate rigid plastics (which tend to be three dimensional) fromplastic film and/or paper, which are generally two-dimensional. Twodimensional plastics including films and rigid materials generally havea thickness less than ⅛ inch. Thus, the 2-dimensional materials areconsidered 2-dimensional because their thickness is much less than theirlength and width (e.g., 10 times or 100 times less). In addition oralternatively, a 2D-3D separator can be used to separate wood (whichtends to be more three dimensional) from textiles (which tends to bemore two dimensional).

Another mechanized sorting apparatus that can be used is an opticalsorter. The optical sorter may be configured to separate film plasticsfrom paper or separate different types of plastics from one another. Forexample an optical sorter can be configured to recover HDPE and/or PETEfrom an intermediate waste stream. One or more optical sorters may alsobe configured to recover #1-7 plastics and/or to remove and/or recoverPVC plastics. The optical sorters may also be used to sort glass from anintermediate stream enriched in small inorganic particles. There aremany types of optical sorter technologies, including, but not limitedto; Near Infrared (NIR), camera color sorters, X-Ray, etc.

Optical sorters can scan the intermediate waste stream and determinewhether the material being analyzed is a particular type of plastic,paper, or glass. The optical sorter upon detecting a particular materialuses air directed through nozzles to eject the targeted/identifiedmaterial to produce one or more recycled products such as recyclablePETE, recyclable HDPE, recyclable film plastic, recyclable #3-7 plasticand/or recyclable paper products.

Any optical sorter known in the art can be used. For example, in oneembodiment the optical sorter can operate by scanning the intermediatewaste stream in a free fall using a camera sensor. The camera sensordetects the material and then air jets may quickly eject the materialwhile in free fall. There are also optical sorters that utilize nearinfrared, X-Ray and other scanning technologies to separate targetedmaterials from mixed streams. Any number of optical sorters can be usedin series or parallel. Manufacturers of optical sorters include TiTechPellenc, MSS, NRT and others.

The mechanical fractionating and sorting of the systems and methodsdescribed herein are particularly useful for extracting high value wastematerials such as paper, plastic, and non-ferrous metals. In prior artsystems these items have been particularly difficult (or practicallyimpossible) to extract and/or sort from mixed solid waste. Conventionalsystems often cannot extract a significant portion of paper, plasticsand/or non-ferrous metals because these materials cannot be extractedusing a magnet. It is well-known to use magnets in traditional mixedwaste processing systems. Magnets are sufficiently inexpensive and canbe used in multiple locations within a system to make their useeconomically viable even when the magnet only extracts a smallpercentage of the ferrous material. However, recovering even ferrousmetal from mixed solid waste is extremely difficult and inefficient dueto the multitude and variety of materials found in mixed solid waste.The typical condition of mixed solid waste, as it is purged from thecollection vehicles and/or transfer trailers, is such that a simplemagnetic device would likely get a very small percentage, under 20%, ofthe available ferrous metal contained in the mixed solid waste streamand any metal recovered in such a fashion would be highly contaminatedby other materials found in mixed solid waste that would be caughtbetween the magnet's surface and the ferrous metal object that wasattached (e.g. paper, plastic, etc.). In contrast, materials such asrecyclable plastics, paper, and non-ferrous metals (e.g. brass) areoften not extracted from mixed waste because the sorting equipment forthese particular materials cannot handle the waste streams as configuredin these systems. Despite the fact that non-ferrous metals and manysorted recyclable plastics typically have a value 5-15 times as much asferrous metals, the industry usually only uses mechanical means toextract ferrous metal. Furthermore, recovery of these higher valuerecyclables such as paper, plastics and non-ferrous metals is plagued bythe same usual conditions of mixed solid waste, in that such recyclablesare so thoroughly mixed and hidden within the large variety of othernon-recyclable items found the mixed waste stream (e.g. organics, inertmaterials, wood, textiles, fines, etc.). Additionally, a large portionof mixed solid waste, especially from residential collection routes andmulti-family dwellings is deposited in plastic bags and discarded.Manually opening bags of trash that would somehow be picked from mixedsolid waste and the subsequent sorting and recovery of any liberatedrecyclables, would be cost prohibitive in all but the mostunderdeveloped Countries. Finally, the highest valuable recyclablecommodities/materials (e.g. PETE plastic, HDPE plastic, #3-7 plastic,aluminum cans, stainless steel, copper, brass, mixed non-ferrous metals)are generally found to be comprised of very small percentages of between0.1% to 4%, on an individual material basis, relative to the overallmixed solid waste stream. Without most or all of the componentsdescribed herein (e.g., preparation, metering, homogenizing andsorting), extracting these high value recyclable materials frommaterials with such low available percentages within the mixed wastestream is nearly impossible to do in an economically viable method.

6. Metering to Control Flow Rates and Burden Depth

Optionally, the methods can also include metering the sized wastestreams and intermediate waste streams throughout the system to achievea desired mass flow and burden depth. In one embodiment, the comminutionapparatus, size separator, density separator, and/or mechanized sortersare separated by one or more conveyors that have variable speedcontrols. The variable speed control can be set to optimize the massflow through the comminution apparatus, size separators, densityseparators, and/or mechanized sorters to optimize the quantity, purity,and/or value of the recyclable materials being recovered from theoverall system by ensuring a metered and evenly distributed presentationof material to the individual devices. One or more sensors positionedupstream, downstream, or within the one or more of the components of thesystem can be used to monitor the separation efficiency, effectiveness,separation purity and/or rate of recovery of the recyclable materials.These values can then be used to optimize or maximize one or moreparameters of the system such as recovery quantity, purity, and/or valueof the recyclable materials recovered. Examples of sensors that can beused to control the flow rate of the waste streams include level sensorssuch as, but not limited to optical sensors and/or ultrasonic sensorsthat measure the height of material building up on a conveyor and/orupstream of a metering device and/or that measure open space on a belt.A belt, metering device, or other piece of equipment can be sped up orslowed down using the sensor data to ensure that a flow rate or desiredburden depth is achieved on a belt or in or through a piece ofprocessing equipment (e.g., size separators) and/or any other portion ofthe system described herein. Other sensors include mechanical switchesthat are physically actuated by the waste stream building up beyond adesired level (e.g., height), which actuates the mechanical switch toprovide a signal that can then be used to regulate flow or burden depth.The speed of all metering equipment including; walking floors;conveyors; metering drums; shredders and grinders; air drum separators;screens of all types; vibratory feeders; metering feeder bins; loadlevelers; and other such devices can be controlled and adjusted viacontrol systems and other devices in order to properly meter materialthrough all portions of the invention. In some embodiments, the meteringcan be critical to obtain the desired high recovery and purity ofrecyclable materials from mixed solid waste.

The systems and methods can include using a plurality of sensors andmetering the flow or depth burden of waste material conveyed to aplurality of sorting apparatuses. Although not required, it ispreferable that each sorting apparatus have a sensor associatedtherewith and that the sensor be used to independently control meteringof the two or more sorting apparatuses. For example, a level sensor orflow sensor can be positioned near an inlet of any combination of3-dimensional sorter, optical sorter, eddy current separator, or thelike.

7. Recovery Rates of Recyclable Materials

The present invention is particularly advantageous for recovering themajority of one or more different types of recyclable materials presentin a mixed solid waste stream. The methods and systems are particularlyuseful where high value recyclables are present in very lowconcentrations. The systems and methods allow processing of mixed wastestream to metaphorically speaking “pick the needle out of the haystack.”In one embodiment, the mixed waste stream may include at least one typeof recoverable material at a concentration less than 15%, less than 10%,less than 5%, or even less than 1%, where the system or method isconfigured to recover at least 50%, at least 70%, at least 80%, or evenat least 90% of the particular recoverable material.

In addition, the methods and systems as described herein may recover atleast 25%, 50%, 75% or 90% of the recyclable metal in the waste stream(by weight) as recyclable metal product having a purity suitable forsale to a merchant of recyclable metals.

The process may recover at least 25%, 50%, 75% or 90% of the recyclableplastic materials in the mixed waste stream (by weight) to yield arecyclable plastic product having suitable purity for sale to a merchantof recyclable plastic products.

The process may recover at least 25%, 50%, 75% or 90% of the recyclablemixed paper products in the mixed waste stream (by weight) to yield arecyclable mixed paper product having a purity suitable for sale to amerchant of recyclable mixed paper.

The process may recover at least 25%, 50%, 75% or 90% of the recyclabledry organic materials to produce one or more (e.g., 1, 2, 3, 4, or more)recyclable dry organic products. The dry organic products may beselected from the group of mixed paper, 3-D plastics, film plastics,textiles, and wood.

The comminuting, size separation, and/or density separation may be usedto produce homogeneous recycle streams that are sufficiently free fromcontamination to be recycled or used without further separation fromother types of components present in the mixed waste and/or that aremarketable as a recyclable product.

II. Systems for Separating Municipal Solid Waste

FIG. 3 illustrates a system 300 that can be used to extract recyclablematerials from a mixed waste stream. In FIG. 3, a mixed solid waste,such as municipal solid waste, is metered to a presorting conveyor 302.Metering may be carried out using a metering drum 304 and an infeedconveyor 306 that receives the mixed solid waste from a walking floorbunker feeder 308. Mixed solid waste on conveyor 302 is transferred toshredder 316. Mixed waste on conveyor 302 may be sorted manually. Forexample, manual laborers may pick large pieces of cardboard that areeasily identifiable and selected out of large volumes of waste. Othermaterials may also be manually picked prior to shredding, includinglarge pieces of treated wood, electronic waste (e.g. eWaste) or otherobviously valuable items that can be efficiently hand-picked orotherwise conveniently pulled from conveyor 302. Picked cardboard may becollected and stored in bin 310 or baled and shipped to a paper mill.Other recyclable materials such as non-ferrous and ferrous metals and/orother sources of recyclable materials may be collected and stored in bin312 or additional bins. In addition, hazardous waste may be collectedand stored in bin 314 and subsequently disposed of in a proper manner.While presorting is not required, pre-sorting can be particularly usefulto avoid contamination from hazardous wastes and potential damage to theshredder from heavy ferrous structural metal, concrete, large stones andother items.

Material from conveyor 302 that is not picked is delivered to shredderor grinder 316 which shreds or grinds the waste to a desired top cut asdescribed above. The shredded material is moved on a conveyor 318 undera suspended magnet 320, which collects ferrous metal exposed in thewaste stream and delivers it to ferrous metal storage 322. Due to burdendepth, the magnet 320 is preferably a suspended drum magnet althoughother magnets may be used alone or in combination with a suspended drummagnet. Drum magnets are advantageous due to the burden depth prior tosize sorting and their ability to capture ferrous metal in flight afterbeing discharged from the conveyor 318 therefore minimizing mostnon-metallic cross contamination of the extracted ferrous metal.

Comminuted waste passing under magnet 320 is delivered to screens 324,which separates the comminuted waste stream by size to produce a firstover fraction and a first under fraction. Screens 324 may include onescreen or a plurality of similar and/or different sized screens andtypes of screens to produce one or more under fractions and one or moreover fractions. The over fraction may be enriched in dry organics andunder fraction may be enriched in wet organics.

The under fraction (i.e., fines) from screens 324 is conveyed onconveyor 326 to a second screen 328. The under fraction (i.e., fines)from second screen 328 may include wet organics and/or heavy inorganicmaterials, which may be processed using an eddy current separator 330 torecover non-ferrous metals. Conveyor 329 may be switchable to direct thefines from screen 328 to conveyor 336 if the inorganic fraction isdominant or to eddy current separator 330 if the wet organic isdominant. The wet organics from eddy current separator 330 can becollected and stored in bin 332 and the non-ferrous metals collected inbin 333.

The over fraction (i.e., coarse) from fine screen 328 may be furtherprocessed in density separator 334 to produce a light fraction having asmall particle size and a heavy inorganic fraction. The heavy inorganicfraction can be conveyed to conveyor 336 and the light fraction canoptionally be loaded in a second density separator 338 for additionalseparation into a light dry organic fraction and a heavy wet organicfraction.

With reference now to the first over fraction (from screen 324), theover fraction is conveyed on conveyor 340 to third density separator342. Third density separator 342 can be configured to produce a lightintermediate stream and a heavy intermediate stream. For example, thirddensity separator 342 may be configured to cut in a range from 8-15 lbs.The light intermediate stream (i.e., less than 8-15 lbs) may be enrichedin dry plastics, paper, light ferrous metals (e.g. tin cans and tin canlids and other light ferrous metal items) and light non-ferrous metals(e.g., aluminum cans and other light non-ferrous items), which aretransferred to conveyor 344.

The heavy intermediate waste stream from third density separator 342(i.e., greater than 8-15 lbs) may be enriched in heavy inorganic andheavy wet organic materials, which are delivered to fourth densityseparator 346 for additional separation. Fourth density separator 346may cut in a range from 60-120 lbs to produce a light intermediatestream, which is delivered to fifth density separator 364. Fourthdensity separator 346 may also produce a heavy intermediate stream(i.e., greater than 60-120 lbs) enriched in heavy inorganic waste, whichis delivered to conveyor 336. The intermediate stream on conveyor 336may be sorted using a suspended drum magnet to collect ferrous metal andthe remainder of the stream loaded on a vibratory feeder 350 that feedsan eddy current separator 352, which separates non-ferrous metal fromthe residue of inorganic waste. The non-ferrous metals may be furtherseparated in infrared or other sorter 381 to extract copper and/or brassfrom other non-ferrous metals (i.e., to produce a mixed non-ferrousproduct stored in bin 396 and a brass and/or copper product stored inbin 398). The non-ferrous metals may be baled and/or bulk stored forshipment to mills.

The remainder of the waste stream exiting eddy current separator 352 isloaded on conveyor 354 and further processed using stainless steelsorter 356 and glass optical sorter 358. The intermediate stream may besorted to extract stainless steel using stainless steel sorter 356and/or sorted to extract glass using optical sorter 358. The sorting canproduce recyclable stainless steel product and recyclable glassproducts, which can be stored in bins 362 and 360, respectively.

With reference again to fifth density separator 364, the lightintermediate stream from separator 346 can be fractionated at a densityof up to 15 lbs for the wood and textiles to 40 lbs-60 lbs for the heavywet organics to produce a light intermediate waste stream enriched inwood and textiles. The wood and textiles can be separated on 2D-3Dsorter such as ballistic or angled disc screen separator 366 toyield-three dimensional recyclable wood product and a two-dimensionalrecyclable textile product, which can be collected in bins 368 and 320,respectively. The heavy stream from separator 364 may be enriched inheavy wet organics and can be delivered to eddy current separator 330and/or joined with waste from separators 328 and 338.

With reference again to conveyor 344, the intermediate light stream fromdensity separator 342 may be processed by suspension magnet 372 to yielda recyclable ferrous metal product collected in bin 373. The portion ofintermediate stream that passes under magnet 372 and onto vibratoryfeeder 374 is loaded into a series of eddy current separators 376 and378, which process the intermediate stream to recover non-ferrousmetals. The non-ferrous metals may be collected on conveyor 377 andcompacted into bales using baler 379 and then stored for shipment.

The dry organics not recovered in eddy current separators 376 and 378provide an intermediate stream enriched in paper and plastics. Theintermediate stream enriched in paper and plastics can be processedusing a 2D-3D separator such as ballistic or angled disc screenseparator 380. Ballistic or angled disc screen separator 380 separatesplastic films and/or paper (i.e., 2D particles) from three-dimensionalparticles such as fractured rigid plastics. The 2D-3D separator can beplaced before or after the eddy current separators 376 and 378.

The two-dimensional materials from ballistic or angled disc screenseparator 380 can be delivered to conveyor 400 and the three-dimensionalmaterial can be further processed using optical sorters. Thethree-dimensional material can be processed in a first optical sorter382 to produce an HDPE plastic product or PETE plastic product or #3-7plastic product that is deposited onto quality control conveyor 383 anddeposited into bin 384 or baled in baler 385. The intermediate streamcan then be processed in a second optical sorter 388 to produce a PETEplastic product or HDPE plastic product or #3-7 plastic product that isdeposited onto quality control conveyor 389 and deposited into bin 386or baled in baler 387. Finally, the intermediate waste stream may beprocessed in a third optical sorter 390 to produce a recyclable #1-7plastics product or HDPE plastic product or PETE plastic product that isdeposited onto quality control conveyor 391 and deposited into bin 392or baled in baler 397. The remainder of the waste stream from opticalsorters 382, 388 and 390 may be a non-recyclable residual material or animproperly sorted recyclable material (e.g., PVC, stones, foam, fragmentof an aluminum can, etc.), which may be collected on conveyor 393 and/orcollected in bin 395 or transfer trailer prior to being disposed of in alandfill or further separated into potentially recyclable fractions ofmixed inorganic material and transformed into various building materialsthat can potentially be marketed or used in construction applications.Quality control points can be placed between the optical sorters andbins as illustrated by quality control points 383, 389, and 391. Thequality control points can be manual or mechanized inspection. Inaddition the materials in bins 384, 386, and 392 may be baled in balers397, 398, and 399, respectively.

With reference now to the two-dimensional material received on conveyor400 from ballistic or angled disc screen separator 380, thetwo-dimensional material may be an intermediate stream enriched in filmplastic and mixed paper. The two-dimensional materials may be loadedinto a dosing bin or other type of metered storage and feeding device402 and then metered to a plurality (e.g., 2-12) optical sorters 404that are configured to separate film plastics from paper. Opticalsorters 404 produce a recyclable plastic film product 406 and arecyclable mixed paper product 408, either or both of which may be baledand/or stored for sale or shipment.

Wet organics produced in system 300 (e.g., wet organics in bin 332) canbe further processed using one or more anaerobic digesters to produce abiogas that can be used as a fuel and/or a compost that can be used as asoil amendment or may be dried to make an organic fuel for combustion asa carbon fuel substitute. A description of suitable microbial digestionsystems that can be used to digest the wet organic waste productproduced in the current method can be found in U.S. Pat. No. 7,615,155entitled “Methods for removal of non-digestible matter from an upflowanaerobic digester,” U.S. Pat. No. 7,452,467 entitled “Induced sludgebed anaerobic reactor,” U.S. Pat. No. 7,290,669 entitled “Upflowbioreactor having a septum and an auger and drive assembly,” and U.S.Pat. No. 6,911,149 entitled “Induced sludge bed anaerobic reactor,” andin U.S. Pat. Pub. No. 2008/0169231 entitled “Upflow bioreactor withseptum and pressure release mechanism,” the entireties of which areincorporated herein by reference.

Wet organics produced in system 300 (e.g., wet organics in bin 332) canbe further processed, composted, provided to or sold to a processor as ahighly concentrated mixed wet organics stream (e.g. food waste and yardwaste and green waste).

The dry organic fuel products can, for example, be used alone or withanother fuel in place of coal and other carbon based fuels in a numberof industrial and energy generation processes. The dry organic fuel canalso be used as a fuel to make synthesis gas through a variety of hightemperature thermal conversion processes (e.g. gasification, plasma arcgasification and pyrolysis.) The dry organic material may also be storedon-site in either a bulk storage building with an automated filling anddischarge system or storage silos with unloading devices.

Those skilled in the art will recognize that the recyclable productsproduced using the methods described herein are highly enriched in aparticular type of recyclable material, which makes the one or moredifferent products useful as a feed material in a recycling process.Nevertheless, the recyclable products are usually not 100% pure. Whilethe recycling industry cannot use raw unprocessed refuse, most recyclingsystems can properly operate with small amounts of impurities. Thesystems and methods of the invention are used to produce recycledproducts having a suitable purity for use in the recycling industry.

While it may be desirable to recover value from essentially all thecomponents of a solid waste stream, the present invention includesembodiments in which all or a portion of the wet organic fraction, dryorganic fraction, or inorganic fraction is not fully separated into arecovered product. For example, in one embodiment all or a portion ofthe wet organic fraction, dry organic fraction, or inorganic fraction,whether mixed, properly separated, or improperly separated may simply belandfilled depending on the purity of the particular fraction and/or themarket conditions for recycling the particular fraction (e.g., film maybe landfilled).

While many of the methods and systems disclosed herein have beendescribed as including density separation, those skilled in the art willrecognize that in some embodiments, sufficient separation can beachieved without density separation, so long as the waste stream iscomminuted and separated by size to produce intermediate streamsenriched in at least one recoverable material.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

We claim:
 1. A method for recovering recyclable materials from mixedsolid waste stream, comprising: providing a mixed waste streamcomprising at least one high value recyclable material selected from thegroup consisting of paper, plastic, and metal, wherein the mixed wastestream includes at least 20% by weight of low value material selectedfrom the group consisting of wet organics, green waste, food waste,grit, fines less than 1 inch, asphalt, concrete, textiles, and wood,rubber, film plastic, PVC, foil, rock, used consumer products, low valueglass, composite materials, and combinations of these; fractionating themixed waste stream by size and by density using a size separator and adensity separator; and sorting at least a portion of the intermediatestreams to produce a plurality of recyclable products.